Imaging lens having four lens elements, and electronic apparatus having the same

ABSTRACT

An imaging lens includes a first lens element, a second lens element, a third lens element, and a fourth lens element arranged from an object side to an image side in the given order. The first lens element has positive refractive power and an image-side surface with a concave portion in the vicinity of an optical axis. The object-side surface of the third lens element has a concave portion in a vicinity of an optical axis of the imaging lens. The object-side surface of the fourth lens element has a convex portion in a vicinity of the optical axis of the imaging lens. The imaging lens does not have any lens element with refractive power other than the first, second, third, and fourth lens elements.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/942,428, filed on Nov. 16, 2015, which is a continuation of U.S.patent application Ser. No. 13/738,313, filed on Jan. 10, 2013, whichclaims priority to Taiwanese Application No. 101130990, filed on Aug.27, 2012, the contents of which are hereby incorporated by reference intheir entirety for all purposes.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an imaging lens and an electronicapparatus, more particularly to an imaging lens having four lenselements and an electronic apparatus having the same.

Description of the Related Art

In recent years, as use of portable electronic devices (e.g., mobilephones and digital cameras) becomes ubiquitous, much effort has been putinto reducing dimensions of portable electronic devices. Moreover, asdimensions of charged coupled device (CCD) and complementary metal-oxidesemiconductor (CMOS) based optical sensors are reduced, dimensions ofimaging lenses for use with the optical sensors must be correspondinglyreduced without significantly compromising optical performance.

In view of the above, each of U.S. Pat. No. 7,355,801 and US PatentApplication Publication No. 20120013998 discloses a conventional imaginglens with four lens elements, of which the image-side surface of asecond lens element is a concave surface.

Japanese Patent Application Publication No. 2011-064989, U.S. Pat. Nos.7,920,340 and 7,777,972, and U.S. Patent Application Publication No.20110058089 also disclose conventional imaging lenses with four lenselements, each of which is spaced apart from an adjacent one of the lenselements by a relatively wide gap. In the fifth embodiment of U.S. Pat.No. 7,9203,40, the lens has a length of 7 mm, which goes against thetrend toward reducing thickness of portable electronic products, such asmobile phones and digital cameras.

Thus, it is apparent that the current trend in development of imagingsystems for portable electronic devices focuses on reducing overalllengths of the imaging systems. However, optical performances andimaging qualities of the imaging systems may be compromised as theoverall lengths are reduced.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide an imaginglens having a shorter overall length while maintaining good opticalperformance.

Accordingly, an imaging lens of the present invention comprises first,second, third, and fourth lens elements arranged from an object side toan image side in the given order. Each of the first, second, third, andfourth lens elements has an object-side surface facing toward the objectside and an image-side surface facing toward the image side.

The first lens element has a positive refractive power, and theobject-side surface thereof is a convex surface.

The second lens element has a negative refractive power, and theimage-side surface thereof has a convex portion in a vicinity of anoptical axis of the imaging lens.

The object-side surface of the third lens element has a concave portionin a vicinity of the optical axis of the imaging lens.

The object-side surface of the fourth lens element has a convex portionin a vicinity of the optical axis of the imaging lens.

The image-side surface of the fourth lens element has a concave portionin a vicinity of the optical axis of the imaging lens, and a convexportion in a vicinity of a periphery of the fourth lens element.

The imaging lens does not include any lens element with refractive powerother than the first, second, third, and fourth lens elements.

Another object of the present invention is to provide an electronicapparatus having an imaging lens with four lens elements.

Accordingly, an electronic apparatus of the present invention comprisesa housing; and an imaging module disposed in the housing, and includingthe imaging lens of the present invention, a barrel on which the imaginglens is disposed, a seat unit on which the barrel is disposed, and animage sensor disposed at the image side and operatively associated withthe imaging lens for capturing images.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiments with reference to the accompanying drawings, of which:

FIG. 1 is a schematic diagram that illustrates the first preferredembodiment of an imaging lens according to the present invention;

FIG. 2 shows values of some optical parameters corresponding to theimaging lens of the first preferred embodiment;

FIG. 3 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the first preferred embodiment;

FIGS. 4(a) to 4(d) show different optical characteristics of the imaginglens of the first preferred embodiment;

FIG. 5 is a schematic diagram illustrating spatial axes;

FIG. 6 is a schematic diagram that illustrates the second preferredembodiment of an imaging lens according to the present invention;

FIG. 7 shows values of some optical parameters corresponding to theimaging lens of the second preferred embodiment;

FIG. 8 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the second preferred embodiment;

FIGS. 9(a) to 9(d) show different optical characteristics of the imaginglens of the second preferred embodiment;

FIG. 10 is a schematic diagram that illustrates the third preferredembodiment of an imaging lens according to the present invention;

FIG. 11 shows values of some optical parameters corresponding to theimaging lens of the third preferred embodiment;

FIG. 12 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the third preferred embodiment;

FIGS. 13(a) to 13(d) show different optical characteristics of theimaging lens of the third preferred embodiment;

FIG. 14 is a schematic diagram that illustrates the fourth preferredembodiment of an imaging lens according to the present invention;

FIG. 15 shows values of some optical parameters corresponding to theimaging lens of the fourth preferred embodiment;

FIG. 16 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the fourth preferred embodiment;

FIGS. 17(a) to 17(d) show different optical characteristics of theimaging lens of the fourth preferred embodiment;

FIG. 18 is a schematic diagram that illustrates the fifth preferredembodiment of an imaging lens according to the present invention;

FIG. 19 shows values of some optical parameters corresponding to theimaging lens of the fifth preferred embodiment;

FIG. 20 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the fifth preferred embodiment;

FIGS. 21(a) to 21(d) show different optical characteristics of theimaging lens of the fifth preferred embodiment;

FIG. 22 is a schematic diagram that illustrates the sixth preferredembodiment of an imaging lens according to the present invention;

FIG. 23 shows values of some optical parameters corresponding to theimaging lens of the sixth preferred embodiment;

FIG. 24 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the sixth preferred embodiment;

FIGS. 25(a) to 25(d) show different optical characteristics of theimaging lens of the sixth preferred embodiment;

FIG. 26 is a schematic diagram that illustrates the seventh preferredembodiment of an imaging lens according to the present invention;

FIG. 27 shows values of some optical parameters corresponding to theimaging lens of the seventh preferred embodiment;

FIG. 28 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the seventh preferred embodiment;

FIGS. 29(a) to 29(d) show different optical characteristics of theimaging lens of the seventh preferred embodiment;

FIG. 30 is a schematic diagram that illustrates the eighth preferredembodiment of an imaging lens according to the present invention;

FIG. 31 shows values of some optical parameters corresponding to theimaging lens of the eighth preferred embodiment;

FIG. 32 shows values of some parameters of an optical relationshipcorresponding to the imaging lens of the eighth preferred embodiment;

FIGS. 33(a) to 33(d) show different optical characteristics of theimaging lens of the eighth preferred embodiment;

FIG. 34 is a table that shows values of parameters of other opticalrelationships corresponding to the imaging lenses of the first to eighthpreferred embodiments;

FIG. 35 is a schematic partly sectional view to illustrate a firstexemplary application of the imaging lens of the present invention; and

FIG. 36 is a schematic partly sectional view to illustrate a secondexemplary application of the imaging lens of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present invention is described in greater detail, it shouldbe noted that like elements are denoted by the same reference numeralsthroughout the disclosure.

Referring to FIG. 1, an imaging lens 10 of the present inventionincludes an aperture stop 2, first, second, third, and fourth lenselements 3-6, and an optical filter 7 arranged in the given order alongan optical axis (I) from an object side to an image side. The opticalfilter 7 is an infrared cut filter for selectively absorbing infraredlight to thereby reduce imperfection of images formed at an image plane8.

Each of the first, second, third, and fourth lens elements 3-6 and theoptical filter 7 has an object-side surface 31, 41, 51, 61, 71 facingtoward the object side, and an image-side surface 32, 42, 52, 62, 72facing toward the image side. Light entering the imaging lens 10 travelsthrough the aperture stop 2, the object-side and image-side surfaces 31,32 of the first lens element 3, the object-side and image-side surfaces41, 42 of the second lens element 4, the object-side and image-sidesurfaces 51, 52 of the third lens element 5, the object-side andimage-side surfaces 61, 62 of the fourth lens element 6, and theobject-side and image-side surfaces 71, 72 of the optical filter 7, inthe given order, to form an image on the image plane 8. Each of theobject-side surfaces 31, 41, 51, 61 and the image-side surfaces 32, 42,52, 62 is aspherical and has a center point coinciding with the opticalaxis (I).

During manufacture, the first lens element 3 may be formed with anextending portion, which may be flat or stepped in shape. In terms offunction, while the object-side and image-side surfaces 31, 32 areconfigured to enable passage of light through the first lens element 3,the extending portion merely serves to provide the function ofinstallation and does not contribute toward passage of light through thefirst lens element 3. The other lens elements 4-6 may also be formedwith extending portions similar to that of the first lens element 3.

The lens elements 3-6 are made of plastic material in this embodiment,and at least one of them may be made of other materials in otherembodiments.

In the first preferred embodiment, which is depicted in FIG. 1, thefirst lens element 3 has a positive refractive power, the object-sidesurface 31 thereof is a convex surface, and the image-side surface 32thereof is a concave surface that has a concave portion 321 in avicinity of the optical axis (I).

The second lens element 4 has a negative refractive power, theobject-side surface 41 thereof is a concave surface, and the image-sidesurface 42 thereof is a convex surface that has a convex portion 421 ina vicinity of the optical axis (I).

The third lens element 5 has a positive refractive power, theobject-side surface 51 thereof is a concave surface that has a concaveportion 511 in a vicinity of the optical axis (I), and the image-sidesurface 52 thereof is a convex surface.

The fourth lens element 6 has a negative refractive power, theobject-side surface 61 thereof is a curved surface that has a convexportion 611 in a vicinity of the optical axis (I) and a concave portion612 in a vicinity of the periphery of the fourth lens element 6, and theimage-side surface 62 thereof is a curved surface that has a concaveportion 621 in a vicinity of the optical axis (I) and a convex portion622 in a vicinity of the periphery of the fourth lens element 6.

Shown in FIG. 2 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the first preferredembodiment. The imaging lens 10 has an overall system focal length of2.01 mm, a half field-of-view (HFOV) of 33.54°, and a system length of2.50 mm.

In this embodiment, each of the object-side surfaces 31-61 and theimage-side surfaces 32-62 is aspherical, and satisfies the opticalrelationship of

$\begin{matrix}{z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}r^{2}}}} + {u^{4}{\sum\limits_{m = 0}^{13}\; {a_{m}{Q_{m}^{con}\left( u^{2} \right)}}}}}} & (1)\end{matrix}$

where:

z represents a depth of an aspherical surface, which is defined as aperpendicular distance between an arbitrary point on the asphericalsurface and a tangential plane at a vertex of the aspherical surface atthe optical axis (I), and the distance between the arbitrary point andthe optical axis (I) is represented as y;

c represents a vertex curvature of the aspherical surface;

K represents a conic constant;

r represents a radial distance, and satisfies a relationship of

${r = \sqrt{x^{2} + y^{2}}};$

u represents r/r_(n), where r_(n) represents a normalization radius(NRADIUS);

a_(m) represents an m^(th)Q^(con) coefficient; and

Q_(m) ^(con) represents an m^(th)Q^(con) polynomial,

where x, y, and z have a relationship there among, as shown in FIG. 5,and the z axis is the optical axis (I).

Shown in FIG. 3 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to thefirst preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the first preferred embodiment are as follows:

G _(aa) /T ₂=1.31

BFL/G _(aa)=3.00

EFL/T ₂=8.15

T ₁ /G ₁₂=4.03

where:

T₁ represents a distance between the object-side surface 31 and theimage-side surface 32 of the first lens element 3 at the optical axis(I);

T₂ represents a distance between the object-side surface 41 and theimage-side surface 42 of the second lens element 4 at the optical axis(I);

G_(aa) represents a sum of a distance between the image-side surface 32of the first lens element 3 and the object-side surface 41 of the secondlens element 4 at the optical axis (I), a distance between theimage-side surface 42 of the second lens element 4 and the object-sidesurface 51 of the third lens element 5 at the optical axis (I), and adistance between the image-side surface 52 of the third lens element 5and the object-side surface 61 of the fourth lens element 6 at theoptical axis (I);

G₁₂ represents a distance between the image-side surface 32 of the firstlens element 3 and the object-side surface 41 of the second lens element4 at the optical axis (I);

BFL represents a distance between the image-side surface 62 of thefourth lens element 6 and the image plane 8 of the imaging lens 10 atthe optical axis (I); and

EFL (effective focal length) represents a system focal length of theimaging lens 10.

FIGS. 4(a) to 4(d) show simulation results corresponding to longitudinalspherical aberration, sagittal astigmatism aberration, tangentialastigmatism aberration, and distortion aberration of the first preferredembodiment, respectively. In each of the simulation results, curvescorresponding respectively to wavelengths of 470 nm, 555 nm, and 650 nmare shown.

It can be understood from FIG. 4(a) that, since each of the curvescorresponding to longitudinal spherical aberration has a focal length ateach field of view (indicated by the vertical axis) that falls withinthe range of ±0.075 mm, the first preferred embodiment is able toachieve a relatively low spherical aberration at each of thewavelengths. Furthermore, since a deviation in focal length among thecurves at each field of view does not exceed the range of ±0.015 mm, thefirst preferred embodiment has a relatively low chromatic aberration.

It can be understood from FIGS. 4(b) and 4(c) that, since each of thecurves falls within the range of ±0.05 mm of focal length, and each ofthe curves corresponding to sagittal astigmatism aberration falls withinthe range of ±0.02 mm of focal length, the first preferred embodimenthas a relatively low optical aberration.

Moreover, as shown in FIG. 4(d), since each of the curves correspondingto distortion aberration falls within the range of ±3%, the firstpreferred embodiment is able to meet requirements in imaging quality ofmost optical systems.

In view of the above, with the system length reduced down to below 3 mm,the imaging lens 3 of the first preferred embodiment is still able toachieve a relatively good optical performance.

FIG. 6 illustrates the second preferred embodiment of an imaging lens 10of the present invention, which has a configuration similar to the firstpreferred embodiment.

Shown in FIG. 7 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the second preferredembodiment. The imaging lens 10 has an overall system focal length of2.10 mm, an HFOV of 32.24°, and a system length of 2.57 mm.

Shown in FIG. 8 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to thesecond preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the second preferred embodiment are as follows:

G _(aa) /T ₂=1.15

BFL/G _(aa)=3.50

EFL/T ₂=7.47

T ₁ /G ₁₂=3.51

FIGS. 9(a) to 9(d) show simulation results corresponding to longitudinalspherical aberration, sagittal astigmatism aberration, tangentialastigmatism aberration, and distortion aberration of the secondpreferred embodiment, respectively. It can be understood from FIGS.9(a), 9(b), 9(c) and 9(d) that the second preferred embodiment islikewise able to achieve a relatively good optical performance even withthe system length reduced down to below 3 mm.

FIG. 10 illustrates the third preferred embodiment of an imaging lens 10of the present invention, which has a configuration similar to the firstpreferred embodiment.

Shown in FIG. 11 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the third preferredembodiment. The imaging lens 10 has an overall system focal length of1.94 mm, an HFOV of 34.48°, and a system length of 2.46 mm.

Shown in FIG. 12 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to thethird preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the third preferred embodiment are as follows:

G _(aa) /T ₂=1.20

BFL/G _(aa)=1.65

EFL/T ₂=5.05

T ₁ /G ₁₂=2.49

FIGS. 13(a) to 13(d) show simulation results corresponding tolongitudinal spherical aberration, sagittal astigmatism aberration,tangential astigmatism aberration, and distortion aberration of thethird preferred embodiment, respectively. It can be understood fromFIGS. 13(a), 13(b), 13(c) and 13(d) that the third preferred embodimentis likewise able to achieve a relatively good optical performance evenwith the system length reduced down to below 3 mm.

FIG. 14 illustrates the fourth preferred embodiment of an imaging lens10 of the present invention, which has a configuration similar to thefirst preferred embodiment.

Shown in FIG. 15 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the fourth preferredembodiment. The imaging lens 10 has an overall system focal length of2.03 mm, an HFOV of 33.85°, and a system length of 2.56 mm.

Shown in FIG. 16 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to thefourth preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the fourth preferred embodiment are as follows:

G _(aa) /T ₂=2.40

BFL/G _(aa)=2.20

EFL/T ₂=11.27

T ₁ /G ₁₂=2.32

FIGS. 17(a) to 17(d) show simulation results corresponding tolongitudinal spherical aberration, sagittal astigmatism aberration,tangential astigmatism aberration, and distortion aberration of thefourth preferred embodiment, respectively. It can be understood fromFIGS. 17(a), 17(b), 17(c) and 17(d) that the fourth preferred embodimentis likewise able to achieve a relatively good optical performance evenwith the system length reduced down to below 3 mm.

FIG. 18 illustrates the fifth preferred embodiment of an imaging lens 10of the present invention, which has a configuration similar to the firstpreferred embodiment.

Shown in FIG. 19 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the fifth preferredembodiment. The imaging lens 10 has an overall system focal length of2.27 mm, an HFOV of 30.57°, and a system length of 2.75 mm.

Shown in FIG. 20 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to thefifth preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the fifth preferred embodiment are as follows:

G _(aa) /T ₂=2.00

BFL/G _(aa)=3.60

EFL/T ₂=12.63

T ₁ /G ₁₂=2.69

FIGS. 21(a) to 21(d) show simulation results corresponding tolongitudinal spherical aberration, sagittal astigmatism aberration,tangential astigmatism aberration, and distortion aberration of thefifth preferred embodiment, respectively. It can be understood fromFIGS. 21(a), 21(b), 21(c) and 21(d) that the fifth preferred embodimentis likewise able to achieve a relatively good optical performance evenwith the system length reduced down to below 3mm.

FIG. 22 illustrates the sixth preferred embodiment of an imaging lens 10of the present invention, which has a configuration similar to the firstpreferred embodiment.

Shown in FIG. 23 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the sixth preferredembodiment. The imaging lens 10 has an overall system focal length of2.03 mm, an HFOV of 33.42°, and a system length of 2.50 mm.

Shown in FIG. 24 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to thesixth preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the sixth preferred embodiment are as follows:

G _(aa) /T ₂=3.20

BFL/G _(aa)=1.61

EFL/T ₂=11.26

T ₁ /G ₁₂=1.83

FIGS. 25(a) to 25(d) show simulation results corresponding tolongitudinal spherical aberration, sagittal astigmatism aberration,tangential astigmatism aberration, and distortion aberration of thesixth preferred embodiment, respectively. It can be understood fromFIGS. 25(a), 25(b), 25(c) and 25(d) that the sixth preferred embodimentis likewise able to achieve a relatively good optical performance evenwith the system length reduced down to below 3 mm.

Referring to FIG. 26, the difference between the first and seventhpreferred embodiments of the imaging lens 10 of the present inventionresides in that:

The image-side surface 32 of the first lens element 3 is a curvedsurface that has a concave portion 321 in a vicinity of the optical axis(I) and a convex portion 322 in a vicinity of a periphery of the firstlens element 3.

Shown in FIG. 27 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the seventh preferredembodiment. The imaging lens 10 has an overall system focal length of2.06 mm, an HFOV of 33.14°, and a system length of 2.55 mm.

Shown in FIG. 28 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to theseventh preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the seventh preferred embodiment are as follows:

G _(aa) /T ₂=2.70

BFL/G _(aa)=1.61

EFL/T ₂=10.91

T ₁ /G ₁₂=3.92

FIGS. 29(a) to 29(d) show simulation results corresponding tolongitudinal spherical aberration, sagittal astigmatism aberration,tangential astigmatism aberration, and distortion aberration of theseventh preferred embodiment, respectively. It can be understood fromFIGS. 29(a), 29(b), 29(c) and 29(d) that the seventh preferredembodiment is likewise able to achieve a relatively good opticalperformance even with the system length reduced down to below 3 mm.

FIG. 30 illustrates the eighth preferred embodiment of an imaging lens10 of the present invention, which has a configuration similar to thefirst preferred embodiment.

Shown in FIG. 31 is a table that lists values of some optical parameterscorresponding to the surfaces 31-61, 32-62 of the eighth preferredembodiment. The imaging lens 10 has an overall system focal length of1.97 mm, an HFOV of 34.38°, and a system length of 2.46 mm.

Shown in FIG. 32 is a table that lists values of some optical parametersof the aforementioned optical relationship (1) corresponding to theeighth preferred embodiment.

Relationships among some of the aforementioned optical parameterscorresponding to the eighth preferred embodiment are as follows:

G _(aa) /T ₂=1.66

BFL/G _(aa)=1.61

EFL/T₂=6.50

T₁ /G ₁₂=2.46

FIGS. 33(a) to 33(d) show simulation results corresponding tolongitudinal spherical aberration, sagittal astigmatism aberration,tangential astigmatism aberration, and distortion aberration of theeighth preferred embodiment, respectively. It can be understood fromFIGS. 33(a), 33(b), 33(c) and 33(d) that the eighth preferred embodimentis likewise able to achieve a relatively good optical performance evenwith the system length reduced down to below 3 mm.

Shown in FIG. 34 is a table that lists the aforesaid relationships amongsome of the aforementioned optical parameters corresponding to thepreferred embodiments for comparison.

When the optical parameters of the imaging lens 10 according to thisinvention satisfy the following optical relationships, the opticalperformance is still relatively good even when the system length isreduced down to below 3 mm:

G _(aa) /T ₂≤3.5   (2)

T ₁ /G ₁₂≤4.1   (3)

1.6≤BFL/G _(aa)   (4)

5≤EFL/T ₂≤16   (5)

When the imaging lens 10 satisfies optical relationship (2), G_(aa) andT₂ fall within an appropriate length range. Otherwise, T₂ may be toosmall, which may render manufacturing of the imaging lens 10 difficult.Preferably, the imaging lens 10 satisfies the relationship ofG_(aa)/T₂≤3.2.

When the imaging lens 10 satisfies optical relationship (3), G₁₂ and T₁fall within an appropriate length range. Otherwise, T₁ may be too largeand not favor reduction of the system length of the imaging lens 10.

When the imaging lens 10 satisfies optical relationship (4), G_(aa) andBFL fall within an appropriate length range. Otherwise, BFL may be toosmall, which may render manufacturing of the imaging lens 10 difficult.When BFL/G_(aa) ranges between 1.6 and 2.1, system length of the imaginglens 10 may be reduced with good optical performance, but BFL isrelatively small and G_(aa) is relatively large. Upon consideration ofbalance between the system length of the imaging lens 10 andmanufacturing technique, the imaging lens 10 is preferable to satisfythe relationship of 2.1≤BFL/G_(aa).

When the imaging lens 10 satisfies optical relationship (5), it favorsreduction of the system length of the imaging lens 10. When EFL/T₂ issmaller than 5, EFL may be too small, which may render manufacturing ofthe imaging lens 10 difficult. When EFL/T₂ is larger than 16, EFL may betoo large and not favor reduction of the system length of the imaginglens 10. When 5≤EFL/T₂<6, focal length may be somewhat small and T₂ maybe somewhat large. Since the second lens element 4 is smaller than thethird lens element 5 and the fourth lens element 6 in the arrangement ofthe system length of the imaging lens 10, thickness of the second lenselement 4 may be reduced. However, a relatively large T₂ does not favoradjustment of thickness of other lens elements, and a relatively smallEFL may render manufacturing of the imaging lens 10 difficult. Althoughsystem length of the imaging lens 10 may be reduced with good opticalperformance when 5EFL/T₂<6, it may result in difficulty of manufacturingtechnique and thickness adjustment of the lens elements. Hence, theimaging lens 10 is preferable to satisfy 6≤EFL/T₂≤13.5.

To sum up, effects and advantages of the imaging lens 10 according tothe present invention are described hereinafter.

1. By virtue of the positive refractive power and the convex object-sidesurface 31 of the first lens element 3, the first lens element 3 is ableto achieve a good light converging capability and to distribute partlythe refractive power of the second lens element 4. Through the concaveportion 321 of the image-side surface 32 of the first lens element 3that is disposed in the vicinity of the optical axis (I), theastigmatism may be corrected.

2. By virtue of the negative refractive power and the convex portion 421of the image-side surface 42 of the second lens element 4 that isdisposed in the vicinity of the optical axis (I), as well as the concaveportion 511 of the object-side surface 51 of the third lens element 5that is disposed in the vicinity of the optical axis (I), aberration andfield curvature may be effectively reduced or eliminated.

3. The designs of the concave portion 621 and the convex portion 622 ofthe image-side surface 62, and the convex portion 611 of the object-sidesurface 61 of the fourth lens element 6 favor reducing field curvature,optical aberration, and chief ray angle, and result in higher systemsensitivity.

4. Through design of the relative optical parameters, such as G_(aa)/T₂,T₁/G₁₂, BFL/G_(aa), and EFL/T₂, optical aberration, such as sphericalaberration, may be reduced or eliminated. Through further design andarrangement of the concave and convex portions of the lens elements 3-6,even when the system length is reduced, optical aberrations may still bereduced or eliminated, resulting in relatively good optical performance.

5. Through the aforesaid eight preferred embodiments, it can beappreciated that the system length of this invention may be reduced downto below 3 mm, so as to facilitate developing thinner relevant productsand promote economic benefits.

Shown in FIG. 35 is a first exemplary application of the imaging lens10, in which the imaging lens 10 is disposed in a housing 11 of anelectronic apparatus 1 (such as a mobile phone), and forms a part of animaging module 12 of the electronic apparatus 1. The imaging module 12includes a barrel 21 on which the imaging lens 10 is disposed, a seatunit 120 on which the barrel 21 is disposed, and an image sensor 130disposed at the image plane 8 (see FIG. 1) and operatively associatedwith the imaging lens 10 for capturing images.

The seat unit 120 includes a first seat portion 121 in which the barrel21 is disposed, and a second seat portion 122 interposed between thefirst seat portion 121 and the image sensor 130. The barrel 21 and thefirst seat portion 121 of the seat unit 120 extend along an axis (II),which coincides with the optical axis (I) of the imaging lens 10.

Shown in FIG. 36 is a second exemplary application of the imaging lens10. The difference between the first and second exemplary applicationsresides in that, in the second exemplary application, the seat unit 120is configured as a voice-coil motor (VCM), and the first seat portion121 includes an inner section 123 in which the barrel 21 is disposed, anouter section 124 that surrounds the inner section 123, a coil 125 thatis interposed between the inner and outer sections 123, 124, and amagnetic component 126 that is disposed between an outer side of thecoil 125 and an inner side of the outer section 124.

The inner section 123 and the barrel 21, together with the imaging lens10 therein, are movable with respect to the image sensor 130 along anaxis (III), which coincides with the optical axis (I) of the imaginglens 10. The optical filter 7 of the imaging lens 10 is disposed at thesecond seat portion 122, which is disposed to abut against the outersection 124. Configuration and arrangement of other components of theelectronic apparatus 1 in the second exemplary application are identicalto those in the first exemplary application, and hence will not bedescribed hereinafter for the sake of brevity.

By virtue of the imaging lens 10 of the present invention, theelectronic apparatus 1 in each of the exemplary applications may beconfigured to have a relatively reduced overall thickness with goodoptical and imaging performance, so as to reduce cost of materials, andsatisfy requirements of product miniaturization. Furthermore,application and configuration of the imaging lens 10 are not limited tosuch.

While the present invention has been described in connection with whatis considered the most practical and preferred embodiment, it isunderstood that this invention is not limited to the disclosedembodiment but is intended to cover various arrangements included withinthe spirit and scope of the broadest interpretation so as to encompassall such modifications and equivalent arrangements.

What is claimed is:
 1. An imaging lens comprising a first lens element,a second lens element, a third lens element, and a fourth lens elementarranged from an object side to an image side in the given order, eachof the first, second, third, and fourth lens elements having anobject-side surface facing toward the object side and an image-sidesurface facing toward the image side, wherein: the first lens elementhas positive refractive power; the image-side surface of the first lenselement comprises a concave portion in a vicinity of an optical axis ofthe imaging lens; the object-side surface of the third lens elementcomprises a concave portion in a vicinity of the optical axis; theobject-side surface of the fourth lens element comprises a convexportion in a vicinity of the optical axis; and the imaging lens does notinclude any lens element with refractive power other than the first,second, third, and fourth lens elements, wherein the imaging lenssatisfies 1.900≤ALT/(G₃₄+T₄)≤2.614, where ALT represents a sum ofthicknesses of all four lens elements along the optical axis, G₃₄represents a distance between the image-side surface of the third lenselement and the object-side surface of the fourth lens element at theoptical axis, and T₄ represents a distance between the object-sidesurface and the image-side surface of the fourth lens element at theoptical axis.
 2. The imaging lens of claim 1, wherein the imaging lensfurther satisfies 0.882≤(G₂₃+G₃₄)/T₄≤2.116, where G₂₃ represents adistance between the image-side surface of the second lens element andthe object-side surface of the third lens element at the optical axis.3. The imaging lens of claim 1, wherein the imaging lens furthersatisfies 1.308≤(T₁+G₁₂+G₃₄)/G_(aa)≤2.219, where T₁ represents adistance between the object-side surface and the image-side surface ofthe first lens element at the optical axis, G₁₂ represents a distancebetween the image-side surface of the first lens element and theobject-side surface of the second lens element at the optical axis, andG_(aa) represents a sum of a distance between the image-side surface ofthe first lens element and the object-side surface of the second lenselement at the optical axis, a distance between the image-side surfaceof the second lens element and the object-side surface of the third lenselement at the optical axis, and a distance between the image-sidesurface of the third lens element and the object-side surface of thefourth lens element at the optical axis.
 4. The imaging lens of claim 1,wherein the imaging lens further satisfies 1.942≤(BFL+EFL)/ALT≤2.593,where BFL represents a distance between the image-side surface of thefourth lens element and an image plane of the imaging lens at theoptical axis, and EFL represents a system focal length of the imaginglens.
 5. The imaging lens of claim 1, wherein the imaging lens furthersatisfies 2.255≤(EFL+T₁)/BFL≤3.278, where EFL represents a system focallength of the imaging lens, T₁ represents a distance between theobject-side surface and the image-side surface of the first lens elementat the optical axis, and BFL represents a distance between theimage-side surface of the fourth lens element and an image plane of theimaging lens at the optical axis.
 6. The imaging lens of claim 1,wherein the imaging lens further satisfies 2.733≤ALT/T₁≤3.311, where T₁represents a distance between the object-side surface and the image-sidesurface of the first lens element at the optical axis.
 7. The imaginglens of claim 1, wherein the imaging lens further satisfies1.417≤(G_(aa)+ALT)/BFL≤2.513, where G_(aa) represents a sum of adistance between the image-side surface of the first lens element andthe object-side surface of the second lens element at the optical axis,a distance between the image-side surface of the second lens element andthe object-side surface of the third lens element at the optical axis,and a distance between the image-side surface of the third lens elementand the object-side surface of the fourth lens element at the opticalaxis, and BFL represents a distance between the image-side surface ofthe fourth lens element and an image plane of the imaging lens at theoptical axis.
 8. An imaging lens comprising a first lens element, asecond lens element, a third lens element, and a fourth lens elementarranged from an object side to an image side in the given order, eachof the first, second, third, and fourth lens elements having anobject-side surface facing toward the object side and an image-sidesurface facing toward the image side, wherein: the image-side surface ofthe first lens element comprises a concave portion in a vicinity of anoptical axis of the imaging lens; the second lens element has negativerefractive power; the object-side surface of the third lens elementcomprises a concave portion in a vicinity of the optical axis; theobject-side surface of the fourth lens element comprises a convexportion in a vicinity of the optical axis; and the imaging lens does notinclude any lens element with refractive power other than the first,second, third, and fourth lens elements, wherein the imaging lenssatisfies 1.900≤ALT/(G₃₄+T₄)≤2.614, where ALT represents a sum ofthicknesses of all four lens elements along the optical axis, G₃₄represents a distance between the image-side surface of the third lenselement and the object-side surface of the fourth lens element at theoptical axis, and T₄ represents a distance between the object-sidesurface and the image-side surface of the fourth lens element at theoptical axis.
 9. The imaging lens of claim 8, wherein the imaging lensfurther satisfies 2.831≤(ALT+T₁)/T₃≤5.843, where T₁ represents adistance between the object-side surface and the image-side surface ofthe first lens element at the optical axis, and T₃ represents a distancebetween the object-side surface and the image-side surface of the thirdlens element at the optical axis.
 10. The imaging lens of claim 8,wherein the imaging lens further satisfies 1.733≤(T₂+T₃+T₄)/T₁≤2.311,where T₁ represents a distance between the object-side surface and theimage-side surface of the first lens element at the optical axis, T₂represents a distance between the object-side surface and the image-sidesurface of the second lens element at the optical axis, and T₃represents a distance between the object-side surface and the image-sidesurface of the third lens element at the optical axis.
 11. The imaginglens of claim 8, wherein the imaging lens further satisfies1.205≤(T₁+G₁₂)/(T₂+G₂₃)≤2.110, where T₁ represents a distance betweenthe object-side surface and the image-side surface of the first lenselement at the optical axis, G₁₂ represents a distance between theimage-side surface of the first lens element and the object-side surfaceof the second lens element at the optical axis, T₂ represents a distancebetween the object-side surface and the image-side surface of the secondlens element at the optical axis, and G₂₃ represents a distance betweenthe image-side surface of the second lens element and the object-sidesurface of the third lens element at the optical axis.
 12. The imaginglens of claim 8, wherein the imaging lens further satisfies1.523≤BFL/G_(aa)≤3.327, where BFL represents a distance between theimage-side surface of the fourth lens element and an image plane of theimaging lens at the optical axis, and G_(aa) represents a sum of adistance between the image-side surface of the first lens element andthe object-side surface of the second lens element at the optical axis,a distance between the image-side surface of the second lens element andthe object-side surface of the third lens element at the optical axis,and a distance between the image-side surface of the third lens elementand the object-side surface of the fourth lens element at the opticalaxis.
 13. The imaging lens of claim 8, wherein the imaging lens furthersatisfies 2.365≤(ALT+G₁₂)/G_(aa)≤4.650, where G₁₂ represents a distancebetween the image-side surface of the first lens element and theobject-side surface of the second lens element at the optical axis, andG_(aa) represents a sum of a distance between the image-side surface ofthe first lens element and the object-side surface of the second lenselement at the optical axis, a distance between the image-side surfaceof the second lens element and the object-side surface of the third lenselement at the optical axis, and a distance between the image-sidesurface of the third lens element and the object-side surface of thefourth lens element at the optical axis.
 14. The imaging lens of claim8, wherein the imaging lens further satisfies1.079≤(T₁+T₂+T₄)/(T₃+G₃₄)≤2.174, where T₁ represents a distance betweenthe object-side surface and the image-side surface of the first lenselement at the optical axis, T₂ represents a distance between theobject-side surface and the image-side surface of the second lenselement at the optical axis, and T₃ represents a distance between theobject-side surface and the image-side surface of the third lens elementat the optical axis.
 15. An imaging lens comprising a first lenselement, a second lens element, a third lens element, and a fourth lenselement arranged from an object side to an image side in the givenorder, each of the first, second, third, and fourth lens elements havingan object-side surface facing toward the object side and an image-sidesurface facing toward the image side, wherein: the image-side surface ofthe first lens element comprises a concave portion in a vicinity of anoptical axis of the imaging lens; the object-side surface of the thirdlens element comprises a concave portion in a vicinity of the opticalaxis; the fourth lens element has positive refractive power; theobject-side surface of the fourth lens element comprises a convexportion in a vicinity of the optical axis; and the imaging lens does notinclude any lens element with refractive power other than the first,second, third, and fourth lens elements, wherein the imaging lenssatisfies 1.900≤ALT/(G₃₄+T₄)≤2.614, where ALT represents a sum ofthicknesses of all four lens elements along the optical axis, G₃₄represents a distance between the image-side surface of the third lenselement and the object-side surface of the fourth lens element at theoptical axis, and T₄ represents a distance between the object-sidesurface and the image-side surface of the fourth lens element at theoptical axis.
 16. The imaging lens of claim 15, wherein the imaging lensfurther satisfies 2.699≤(BFL+G_(aa))/(G₁₂+T₄)≤4.451, where BFLrepresents a distance between the image-side surface of the fourth lenselement and an image plane of the imaging lens at the optical axis,G_(aa) represents a sum of a distance between the image-side surface ofthe first lens element and the object-side surface of the second lenselement at the optical axis, a distance between the image-side surfaceof the second lens element and the object-side surface of the third lenselement at the optical axis, and a distance between the image-sidesurface of the third lens element and the object-side surface of thefourth lens element at the optical axis, and G₁₂ represents a distancebetween the image-side surface of the first lens element and theobject-side surface of the second lens element at the optical axis. 17.The imaging lens of claim 15, wherein the imaging lens further satisfies3.525≤EFL/G_(aa)≤6.481, where EFL represents a system focal length ofthe imaging lens, and G_(aa) represents a sum of a distance between theimage-side surface of the first lens element and the object-side surfaceof the second lens element at the optical axis, a distance between theimage-side surface of the second lens element and the object-sidesurface of the third lens element at the optical axis, and a distancebetween the image-side surface of the third lens element and theobject-side surface of the fourth lens element at the optical axis. 18.The imaging lens of claim 15, wherein the imaging lens further satisfies1.451≤(BFL+T₁)/(T₂+G₃₄)≤2.737, where BFL represents a distance betweenthe image-side surface of the fourth lens element and an image plane ofthe imaging lens at the optical axis, T₁ represents a distance betweenthe object-side surface and the image-side surface of the first lenselement at the optical axis, and T₂ represents a distance between theobject-side surface and the image-side surface of the second lenselement at the optical axis.
 19. The imaging lens of claim 15, whereinthe imaging lens further satisfies 3.112≤EFL/(G₂₃+T₃)≤4.837, where EFLrepresents a system focal length of the imaging lens, G₂₃ represents adistance between the image-side surface of the second lens element andthe object-side surface of the third lens element at the optical axis,and T₃ represents a distance between the object-side surface and theimage-side surface of the third lens element at the optical axis. 20.The imaging lens of claim 15, wherein the imaging lens further satisfies1.740≤(ALT+G₁₂)/(G₃₄+G_(aa))≤3.550, where G₁₂ represents a distancebetween the image-side surface of the first lens element and theobject-side surface of the second lens element at the optical axis, andG_(aa) represents a sum of a distance between the image-side surface ofthe first lens element and the object-side surface of the second lenselement at the optical axis, a distance between the image-side surfaceof the second lens element and the object-side surface of the third lenselement at the optical axis, and a distance between the image-sidesurface of the third lens element and the object-side surface of thefourth lens element at the optical axis.